After my engine runs for 10-20 minutes it is not unusual to experience a pronounced engine studder when accelerating through 2500RPM at mid throttle. (Think rush hour traffic.) Doesn't happen every time. Once it starts it occurs independant of throttle position - if I open it wide open it still occurs.

Studder goes away by about 3300RPM. I don't experience it when driving in a the "spirited" fashion and shifting out between 4000-6000. In that mode the RPMS never fall into the sub 3000 Range.

Reminds me of water in the fuel.

Recent Engine mods: Pop Charger, UD Pulleys, Jet computer mod, headers, 60k maintenance, spark pugs.

 

which was the most recent?

 

All part of a single update at Z Motorsports...

 

have you asked them to look at it since they obviously messed it up?

 

Two things?????

First, I've heard some of the aftermarket air filters cause a studder due to turbulence in the maf. I have a slight off-idle studder that wasn't there before I put my k&n on. There's something on the 300zxclub forums about putting duct tape somewhere over the filter.

Second, your egr valve is supposed to start opening up at around 2500 rpm. If the egr diaphragm is bad, you will have a vaccum leak in that rpm range

 

CC - what kind of bizarre advice is THAT?!?

I may be new, but I'm starting to learn about the twisted jokes you guys play on each other.. A human CAN NOT REACH the EGR - its crammed between the engine and the firewall. I guess I could get a cutting toarch and start somewhere around the driver's seat and cut forward . . . or remove the engine . . . or maybe get some dentist tools and try that . . . *JK!*

After multiple tries, I finally FOUND the EGR. If I hang, suspended from a rope and REEEEEEACH behind the engine, lacerating my forarms, I can just barely TOUCH the diaphram. Now, being the enterprising type that I am, I thought, "I'll just trace that hose to a more accessable place and test it there." But it snakes directly underneath the intake manifold! Ugh.

Ha ha. OK, the joke is on me. How DOES a mere mortal test the EGR diaphram? Anyone?

And while we are on the topic, where do you check the vacuum pressure to see if there are leaks? What is a normal reading - at idle, 3000rpm, etc?

 

here ya go .......... SMAK (SMart *** Kid) RTFM (Read The F**k'g Manual) haha j/k

Section EF / EC of the FSM addresses this. The vaccum line from the egr valve goes to the egr control solenoid valve. It's on the right side of the motor towards the front. This might be the place that you want to check the egr at. The egr solenoid does not send a vaccum signal to the egr valve until the 2500-3000 rpm range. This is why you need to check the egr diaphragm independently.

The FSM says that you can check for a vaccum leak by pinching off the air intake hose that goes to the pcv valve. If you pinch this hose off and the engine speed rises, you then have a vaccum leak. The fsm also addresses how to check the egr solenoid for proper function. If your egr valve is not closing all of the way, due to carbon buildup, it will show up as a vaccum leak. faik, you have to remove the motor to get to the egr valve.

I believe on a n/a motor, that you should have around 22 hg. of vaccum @ idle @ sea level. It goes down from there as rpm's increase.

I only bring up the egr system because it is often overlooked in trouble diagnosis and is a common problem with high mileage engines.

 

Excellent advice, CC. Much better than bungie jumping into my engine. :-) BTW - where can I get a copy of the FSM?

 

https://www.zdriver.com/showthread.php?t=8434

2nd topic from the top ...................... Thank Rizz.

 

If you wind up having to replace the EGR valve, instead of doing some kid of Mission Impossible style vertical bungee stunt, you can remove the upper and lower plenum. That will give you access to the EGR valve. If you do that, then you may want to consider honing your upper and lower plenums. If you haven't replaced the timing belt, then this would be a good time to do that also since the upper idler pulley mounting stud is threaded into the lower plenum. It's a wonderful design.

 

To let folks know, I finally got to the bottom of this issue. I found that the TIMING was off so much that it caused this behavior. The needed adjustment required me to rotate the CAS to counter clockwise about 3/8".

What got me thinking along these lines was a post indicating the timing on the 96 at idle is 10 btdc and 90-95 was 15 btdc. Could it possible that the mechanic didn't know that? Dunno, but it works much smoother now.

Thanks for all of the great suggestions. I also found that cleaning out the throttle bodies is quite helpful.

My next step is to check for vacuum leaks. Anyone ever tried the BoostPro Leak Tester? http://www.boostpro.net/prodz32tester.html It looks like a valuable tool.

 

wow thats pretty cool

i think i might have to invest in one of those

 

Now that IS a handy little device, I too may have to invest in one in the future.

Im glad Rizz added the carfiche.com to the list, i didnt even know he had. Ill have to thank my friend for directing me there.